1. Field of the Invention
This invention relates to the field of Spatial Light Modulators (SLMs). More specifically, this invention relates to liquid crystal SLMs, SLM fabrication processes, and SLM packaging methods wherein a cover glass, a semiconductor circuit chip, such as a VLSI chip, and a substrate member are jointed together in a controlled and accurate positional relationship. Devices of this type are sometimes called silicone backplane liquid crystal SLMs wherein detectors, electronic logic, and modulators are integrated into a single device.
2. Description of Related Art
As is well known, SLMs are generally used to impress information on an optical wavefront. Specific uses include coherent optical processing applications, data routing, data input to optical processing systems, high definition visual information display, optical pattern correlators, optoelectronic processing systems, and optical image processing.
Ferroelectric Liquid Crystals (FLCs) have been used in SLMs because of the high birefringence and low voltage operation that is provided by this type of liquid crystal. The properties of FLCs allow large pixel arrays to be constructed that operate at gigabit per second data rates.
It has been suggested that FLC/SLM pixel array devices (i.e., an X-Y coordinate system array of individual pixels) be constructed and arranged using a semiconductor circuit chip to provide the multiple circuit elements that control the state of the multi- pixel FLC layer (i.e., control the state of the FLC layer in the areas of the individual pixels of the SLM array). For example, U.S. Pat. No. 5,073,010 by K. M. Johnson et al, incorporated herein by reference, describes an optically-addressable SLM wherein the SLM's light-sensitive member comprises an integrated circuit substrate that includes a discrete photosensitive area, processing electronics, and a metal crystal modulating pad for each pixel of the SLM, the metal pads being in physical contact with the corresponding pixel areas of a distorted helix FLC.
Another example of the use of a semiconductor substrate in a SLM is U.S. Pat. No. 5,130,830 wherein a spatial light modulator includes a ferroelectric liquid crystal confined between two alignment films and in a cavity that is established by spacers, and wherein a semiconductor substrate includes a photodiode.
A feature of the invention includes the use of solder reflow to produce device alignment. A feature of this general type is shown, for example, in U.S. Pat. No. 4,867,543 wherein a spatial light modulator includes an integrated circuit structure that is aligned to an adjacent modulator array by way of solder bumps, these solder bumps also functioning as circuit connections. U.S. Pat. No. 5,221,989 is also of general interest relative to this feature in that it describes the use of flip chip solder bonds in a SLM using ceramic PLZT.
While the work of others has been generally satisfactory for the limited stated purposes, the art has failed to provide a SLM, or a SLM fabrication technique, wherein the liquid crystal cavity, or gap that exists between a cover glass and a semiconductor chip, is provided in the range of a micron thick, with submicron gap uniformity throughout the cavity. In addition, a structure and arrangement that facilitates use of all four sides of the semiconductor chip for wire bonding to an underlying substrate member has not been provided.